Genetic signatures of variation in population size in a native fungal pathogen after the recent intensive plantation of its host tree

Historical fluctuations in forests’ distribution driven by past climate changes and anthropogenic activities can have large impacts on the demographic history of pathogens that have a long co-evolution history with these host trees. Using a population genetic approach, we investigated that hypothesis by reconstructing the demographic history of Armillaria ostoyae, one of the major pathogens of the maritime pine (Pinus pinaster), in the largest monospecific pine planted forest in Europe (south-western France). Genetic structure analyses and approximate Bayesian computation approaches revealed that a single pathogen population underwent a severe reduction in effective size (12 times lower) 1080–2080 generations ago, followed by an expansion (4 times higher) during the last 4 generations. These results are consistent with the history of the maritime pine forest in the region characterized by a strong recession during the last glaciation (~19 000 years ago) and massive plantations during the second half of the nineteenth century. Results suggest that recent and intensive plantations of a host tree population have offered the opportunity for a rapid spread and adaptation of their pathogens

Latest advances and future perspectives in Armillaria

The basidiomycete genus Armillaria s.l. (Armillaria s.s. and Desarmillaria) has a worldwide distribution and plays a central role in the dynamics of numerous woody ecosystems, including natural forests, tree plantations for timber production, orchards, vineyards and gardens. Early studies have shown that all Armillaria species are capable of degrading dead woody substrates, causing white rot. Moreover, most species exhibit a parasitic ability, and can be considered as facultative necrotrophs. Although over the years extensive research has been conducted on the phylogeny, biology and ecology of different Armillaria species, numerous theoretical and applied questions remain open. Recently published studies have provided new perspectives, the most significant of which we present in this review. First, new investigations have highlighted the importance of a multilocus approach for depicting the phylogeny of the genus Armillaria. Second, the importance of clonality and sexuality for the different species is now better described, enabling a more accurate prediction of population dynamics in various environments. Third, genome sequencing has provided new insights into genome evolution and the genetic basis of pathogenicity and wood degradation ability. Fourth, several new studies have pointed out the possible influence of climate change on Armillaria distribution, biology and ecology, raising questions regarding the future evolution of Armillaria species and their effect on ecosystems. In this review, we also give a state-of-the-art overview of the control possibilities of parasitic Armillaria species. Finally, we outline some still open questions in Armillaria research, the investigation of which will strongly benefit from recent methodological advances

The fungus Armillaria bulbosa is among the largest and oldest living organisms

ASEXUALLY reproducing organisms occur in a variety of taxa in all biological kingdoms1 and distinguishing asexually propagated genotypes is essential for the understanding of their population biology. Among the higher fungi, however, the clonal \u27individual\u27 is especially difficult to define2 because most of the fungal thallus consists of a network of anastamosing hyphae embedded in the substratum. Whether fruit-bodies, the most recognizable part of a fungus, are produced by a single supporting mycelium can only be determined by establishing direct physiological continuity or genetic identity. We report a means by which individual fungi can be unambiguously identified within local populations and identify an individual of Armillaria bulbosa that occupies a minimum of 15 hectares, weighs in excess of 10,000kg, and has remained genetically stable for more than 1,500 years. © 1992 Nature Publishing Group